(1) Field of the Invention
This invention relates to paper feeders for facsimile machine, printers, scanner, etc., in particular to a paper guide for automatic paper feeders.
(2) Description of the Related Art
Traditional automatic paper feeder for a scanner is shown in FIG. 1. A sheet of paper P to be scanned is fed from the left side through a continuous paper guide, having an upper surface 11U, a lower surface with two supporting blades 11L and 11R and a resilient transparent thin film auxiliary scan window 10. The scanned light beam 13 is reflected from the paper to an image sensor 12. The scanned paper then recoils out of the lower right-hand blade 11R of the guide. Below the guide section 99 houses the main frame of the scanner 88, which has a larger transparent scan window 14 used for flat-bed scanning. The first scanning section F provides enough area for the automatic paper feed scanning function. The second scanning section S provides adequate scanning area for flat-bed scanning. Papers are fed intermittently from the left-hand side through the guide blade 11L, resilient film 10 and guide blade 11R automatically.
In such a traditional guide section, the transparent film 10 is constantly being rubbed during scanning operation. After long periods of time, the transparent film becomes blurred due to constant rubbing and the quality of the image deteriorates. Then the film 10 must be replaced. At the same time, since the left-hand guide blade 11L, the film 10 and the right guide blade 11R form a unitary structure which is inaccessible, the dirt residing on the film 10 cannot be wiped off easily.
An object of this invention is to provide a guide for an automatic paper feeder which provides smooth passage of the paper being scanned. Another object of this invention is to provide a paper guide which can easily be cleaned.
These objects are achieved by using separate lower blades for the paper guide, which are separated from the scan window. At the same time the scan window is made of durable glass.
When the scanner is used for both flat-bed scanning and automatic paper feed scanning, the image sensor position should be changed to accommodate for the difference in distance from the image sensor from the scanned paper. Due to the extra scan window used for the automatic paper feeding mechanism, the paper is scanned at a plane higher than that for the flat-bed window. If the extra scan window is thick, provision is made to move the image sensor up so that the light beam reflected from scanned paper has equal length for both the automatic paper feed scanning and the flat-bed scanning. When the extra scan is very thin, it may not be necessary to change the elevation of the image sensor.